In recent years, in an inside air mode in which an air in a vehicle interior air (hereinafter referred to as inside air) is circulated in winter, a need to ensure an anti-fogging property is increasing.
However, in a vapor compression type refrigeration cycle generally used in a vehicle air conditioning apparatus, when an outside air temperature is low like in winter, particularly when traveling at a high speed, a refrigerant cooling capacity of a condenser (that is, a capacity to condense and liquefy a refrigerant) becomes too high and a refrigerant pressure on a high-pressure side becomes too low. In the refrigeration cycle, when the refrigerant pressure on the high-pressure side becomes too low, a differential pressure between the high-pressure side and the low-pressure side decreases, a refrigerant discharge amount of a compressor decreases, and a refrigerant circulation amount of the refrigeration cycle severely decreases.
When the inside air mode is selected in such a state, the inside air high in temperature (for example, 25° C.) suctioned into an evaporator leads to a high heat load, the refrigerant pressure on a low-pressure side rises, and the differential pressure between the high-pressure side and the low-pressure side further decreases. As a result, the amount of liquid refrigerant stagnant in the condenser increases, a flow rate of the refrigerant fed to the evaporator decreases, the evaporator falls into a gas deficient state, a refrigerant distribution is deteriorated, and a dehumidification capacity decreases due to an increase in the superheat amount. Therefore, an absolute humidity of the air conditioning wind used for defogging rises, and the window glass becomes foggy.
Further, when the outside air temperature further drops, the differential pressure between the high-pressure side and the low-pressure side is eliminated, the refrigeration cycle collapses, the evaporator dehumidification capacity is lost, and the window glass may suddenly become fogged during traveling.
For example, Patent Literature 1 has proposed a refrigeration cycle device that is capable of being switched between a refrigeration cycle mode and a thermosiphon mode.
The refrigeration cycle device disclosed in Patent Literature 1 includes, as basic components, a compressor that compresses a refrigerant, a condenser that cools and condenses the refrigerant with a vehicle exterior air (hereinafter referred to as outside air), an evaporator that performs a heat exchange between the refrigerant and the inside air to cool the inside air, and an electric expansion valve for reducing a pressure of the refrigerant.
Further, the refrigeration cycle device disclosed in Patent Literature 1 further includes a bypass passage that bypasses the compressor, and a check valve that opens the bypass passage when the compressor stops. When the thermosiphon mode operation is performed, the compressor is stopped to open the check valve, an electric expansion valve is opened, and the refrigerant is circulated between the condenser and the evaporator to perform heat transfer.
In the refrigeration cycle mode, when the outside air temperature is low as in winter, the condenser refrigerant cooling capacity becomes too high, the refrigerant circulation amount decreases, and the dehumidification capacity decreases. However, in the thermosiphon mode, even when the outside air temperature is low like in winter, the refrigerant can be circulated between the condenser and the evaporator to perform heat transfer, the inside air is cooled down to a dew point temperature or lower, and moisture in air can be condensed and dehumidified. This makes it possible to prevent the window glass from being fogged.